In a number of modern industrial processes it is necessary to etch materials uniformly. The etching may be confined to the material, or the etching process may be continued until the material is etched through, thereby exposing an underlying material. In many industrial applications such as, for example, the fabrication of electronic, optical or optoelectronic workpieces, the etching steps form a very critical phase of workpiece fabrication, as the etching process typically dictates the accuracy to which the workpieces are ultimately manufactured.
There are often more than one hundred processing steps in the fabrication of semiconductor chips, including oxidation, diffusion, ion implantation, deposition of conductors and insulators, photolithography and etching. Various conducting and insulating layers are deposited uniformly over the wafer to a thickness of a few microns. In critical applications, certain new or used parts of semiconductor processing equipment need to be cleaned prior to installation and use in order to remove residual contamination from the initial machining or manufacturing process, or from the processing steps, in order to achieve levels of cleanliness similar to the semiconductor wafer itself and have its surface morphology restored. Furthermore, after many wafers have been processed, the equipment used in the semiconductor processing process becomes contaminated or deposits build-up and therefore becomes unusable.
For example, in an etching machine, polymer deposits on the outer circumference of electrodes or chucks supporting the wafers until it becomes thick enough to interfere with the wafer's contact with the electrode. This results in non-uniform etching across the wafer as well as missed transfers due to a wafer sticking to polymer buildup on the electrode. Non-uniformity exceeding seven percent is beyond some specified limits, in turn affecting side wall profile variance across the wafer. In addition, other components in the equipment chamber, e.g. roofs/domes and liners are also coated with polymers and contaminants which contribute particles, metallic and organic impurities to the wafers. Therefore, it is then necessary to disassemble the parts in the equipment chamber and clean the individual parts. Most types of dry processing equipment used for the manufacture of semiconductor devices utilize processes involving high temperatures, plasmas and gaseous mixtures for film deposition and etching. During these manufacturing processes, organic and inorganic by-products are deposited on the surfaces of workpiece parts.
Some apparati and devices are commercially available to etch workpieces, however, none is ideal. FIG. 1 shows a representative small-scale apparatus 100 of the prior art used to ultrasonically etch a semiconductor fabricationworkpiece 102. An acidic solution 110 is placed into inner container 104 and ultrasonically agitated through aqueous solution 120 held in outer container 130. The entire apparatus is contained within an exhaust hood 150 for the capture of gases 140 that are emitted from the aqueous and acidic solutions as the etching reaction occurs. While representing an advance over earlier etching processes that did not include a concentrated acid or an ultrasonicator, apparatus 100 does not provide the ability to rotate workpiece 102 or create safe working conditions. Nor does apparatus 100 have capability to contain the gases or prevent unwanted components, e.g. impurities from environment and aerosol gases from the aqueous solutions, from entering the etching solution during the etching process, or to increase the partial pressure of the volatilized etching solution and to prevent change in the concentration of the etching solution due to aerosol or volatilisation losses. It also lacks a heating mechanism, probe, etc for regulating the temperature and a ultrasonic buffer for dampening and diffusing the energy for better control over the etch process.
Prior art apparatus 200 shown in FIG. 2 contains two beakers 202 and 204, which contain deionized water that is provided through opening 206, and which overflows into the beakers, which then overflows into the sonication tank 210. Ultrasonication transducer 220 is connected to power oscillator 220 to provide ultrasonic energy to the deionized water. This apparatus lacks a number of desired features, including, most significantly, the ability to contain an acid, the ability to rotate a workpiece being sonicated, a heating element, and an ultrasonic diffuser.
U.S. Pat. No. 6,199,563, which is incorporated by reference herein, adds a modest improvement to ultrasonicators of the prior art by including a rotational mechanism for sonicating a workpiece in an acid solution, but it fails to provide means for containing the acidic gases, preventing unwanted contaminants from the aqueous solution and/or rotational mechanism wear and tear from entering the acidic solution, the ability to increase the partial pressure of the acidic solution, or provide a safer working environment.
What is needed is a method and apparatus for containing the gases produced during ultrasonic agitation, minimizing exposure of the etching solution to the immediately surrounding environment which would thus prevent unwanted contaminants from the aqueous solution and/or rotational mechanism wear and tear from entering the etching solution during the etching process, the ability to increase the partial pressure of the etching solution which would inhibit the formation of dangerous vapors by keeping them in a liquid state, keeping the concentration of the etching solution stable, and the ability to provide a safer working environment. The present invention is designed to meet these needs by providing a more efficient, contaminant-free apparatus and method than those currently available such that semiconductor workpieces can be effectively cleaned and recycled to reduce manufacturing costs.